If all your app services are in one resource group, you can use the following query in Log Analytics to capture any App Service that is down within that specific
resource group. You can always modify the query to add other resource groups if your app services are hosted across multiple resource groups.

As a pre-requisite for this you need to ensure of creating Availability tests for all of your 120 app services (one time manual activity for existing and every
other new app service you are adding as well, as Availability tests are usually configured on a per resource basis for Application Insights, and there is no means of doing this for multiple resources at once in bulk). You can choose this option if you don’t
want to create a new Log Analytics workspace and use the existing application insights instance. Additional documentation reference for creating Availability Tests:
https://docs.microsoft.com/en-us/azure/azure-monitor/app/monitor-web-app-availability(However, you might want to explore the programmatic way of doing this with a script that can fetch all the App service
resources in the specified resource groups and creating alerts through Azure CLI or other means.)

Assuming all of your App Services have Availability Tests configured and sending data to Application Insights, you can use the following query:

Average Response Time of a resource can be checked under the Overview blade of the selected App Service. Within “Metrics” Blade of the App Service, you can “Add Metric” with filters
to Resource, Metric Namespace (App Service standard Metrics) and Metric (Average Response Time). Understand that it is a manual activity to add filters for all your App Services. Time range and Time Granularity can also be adjusted for the same. Once you have
all the necessary resources added, you can click on the "Pin to Dashboard" button to have the graph displayed on the desired dashboard. This would look something like the following picture.

If you are sending the data of all App Services to Application Insights you can use the below sample query and pin it to the dashboard.

4. There are various options provided for setting the Time range and Granularity in the Metric graphs. Attached is the screenshot for the same.

For metrics related graphs from App Services, you can set the interval to 1 hr. And for any queries for Log Analytics/Application Insights you can set
the bin(timestamp)to 1hr. For periodic interval data of every 4Hr, you can possibly use bin(timestamp, 4h). However, you cannot use 4hr, 8hr, 12Hr on the same query and get a single graph.